This invention relates to a method and apparatus for the purification of water, and more specifically, to a method and apparatus utilizing ultraviolet radiation and ozone in combination to inactivate bacteria and certain viruses and to oxidize undersirable compounds in water.
The bactericidal effect of ultraviolet radiation is well-known. The absorption by living cells of ultraviolet radiation of a particular wave length has deleterious effects upon those cells, most notably the inhibition of cell division. In general, ultraviolet radiation of wavelengths in the neighborhood of 2,600 Angstroms has the greatest bactericidal effect.
The disinfecting action of ozone is also well-known and has been used to destroy bacteria and certain viruses in drinking water. Ozone also readily oxidizes many of the compounds which give contaminated water its bad odor and taste.
Ozone is most efficiently produced by subjecting ordinary oxygen to electrostatic discharge. Ozone is also produced less efficiently by subjecting ordinary oxygen to ultraviolet radiation. The absorption by ordinary oxygen of ultraviolet radiation of wavelengths in the neighborhood of 1,850 Angstroms results in the production of ozone.
The combination of the bactericidal effects of ozone and ultraviolet radiation have been utilized to purify liquids, including water. In most such applications an electric discharge is utilized to to produce ozone from ordinary oxygen. The substance to be purified, e.g., water, is passed in the vicinity of an ultraviolet radiation source during which the ultraviolet radiation, restricted to a relatively narrow wavelength range, inactivates bacteria and certain viruses in the liquid. The ozone produced by the ozone generator is then subsequently introduced to the liquid after it has been subjected to the ultraviolet radiation to further inactivate any residual bacteria or viruses.
The above-described method of utilizing both ultraviolet radiation and ozone to purify water has never become commercially feasible, at least for general consumer applications such as swimming pools and potable water supplies, because the requirement of a separate electric-discharge ozone generator and an ultraviolet radiation source renders this method cost prohibitive.
In U.S. Pat. No. 3,336,099, water is passed through a first chamber surrounding an ultraviolet radiation source, and oxygen is passed through a second chamber near the ultraviolet radiation source to produce ozone. The previously irradiated water and the ozone are then mixed together in a third chamber where the ozone acts upon residual bacteria and viruses not destroyed by the ultraviolet radiation.
A recent technique for the removal of cyanides in water involves introducing ozone to the water to be purified while simultaneously irradiating the ozone and water mixture with ultraviolet radiation. Such a technique takes advantage of a catalytic effect of the ultraviolet radiation upon the reaction of ozone wih undesirable substances in the water, such as cyanides. The ultraviolet radiation thus increases the reaction rate of the ozone upon these undesirable compounds over the rate which could be achieved absent the ultraviolet radiation. This technique, as disclosed in U.S. Pat. No. 3,920,547, utilizes a separate electric discharge type of ozone generator to produce ozone. The ozone produced is introduced into the water after which the ozone and water mixture is subjected to the ultraviolet radiation. This form of simultaneous application of ozone and ultraviolet radiation, each of which alone is a strong disinfectant, has also been shown to kill bacteria much faster and at much lower dosages than either ozone or ultraviolet radiation alone. See Prengle, H. William, "Evolution of the Ozone/UV Process For Wastewater Treatment", paper presented at the IOI/EPA colloquium on Wastewater Treatment and Disinfection with Ozone held in Cincinnati, Ohio, Sept. 15, 1977.